1. Field of the Invention
The present general inventive concept relates to a receiver usable in a wire communication or a wireless communication and a transient signal compensation digital signal processor that may be used in the receiver, and methods thereof.
2. Description of the Related Art
FIG. 1 is a diagram exemplifying a physical layer signal used in a general high speed packet communication. The physical layer signal used in the general high speed packet communication may be divided into four portions including a preamble, a header, a payload and a tail. The preamble is used for estimations required for a receiver to receive the physical layer signal, and the header includes a summary of information on the payload that immediately follows the header. The payload includes an information of an upper layer including a user data that is to be actually transmitted in the high speed packet communication, and the tail is an additional signal for managing different types of impairments that may be generated in a channel such as a CRC (cyclic redundancy check) or ECC (error correction code). Therefore, since three parts other than the payload correspond to an additional signal for transmitting the payload more reliably in the channel where the impairment may exist, the three parts are referred to as an overhead. For example, the overhead is a portion of an entirety of the packet that does not include information of a user. It is preferable that the overhead is minimized, and increasing a ratio of the payload to (preamble+header+payload+tail), which is an effective data transmission index of the packet, is a very important technology object of a high speed packet communication standardization.
The preamble generally occupies the largest part of the overhead. The receiver should estimate a plurality of characteristics of a received signal that passes through a physical channel using the preamble in order to reliably demodulate the signal. A first operation that is generally carried out by the receiver after receiving the preamble is a received power estimation and a reception gain control. A range of a signal strength for an optimized performance exists it an actual receiver. In an analog circuit, the optimized performance is achieved in a predetermined voltage range. A predetermined voltage range should be applied to an ADC (analog-to-digital converter) to secure a quality of a converted signal. In a digital signal processor carrying out a fixed point operation, the optimized performance is achieved in a predetermined number range. Therefore, an accurate reception gain control is very significant in a digital demodulation receiver. The signal having the reception gain thereof controlled is subsequently subjected to multiple operations such as a frequency offset estimation, a channel estimation, a timing recovery and a carrier recovery using the preamble. Generally, since an accuracy of a properly designed estimator increases as an estimation time thereof is longer, a reliable estimation is possible only when an appropriate time is given to each estimation. Therefore, a rapid processing of the reception gain control in a short preamble section is very important in the receiver of the high speed communication.
FIG. 2 is a diagram illustrating an example of a related art closed loop gain control.
The received signal is amplified or attenuated to a proper voltage range by passing through a programmable gain amplifier 10 and then input to an analog filter circuit 11. A signal being outputted from the analog filter circuit 11 is applied to an ADC 13 via a programmable gain amplifier 12. An analog signal is converted to a digital fixed point signal using the ADC 13. The converted signal is applied to a decoder 17 via digital signal processors 14, 15 and 16. A digital filter may be used as the digital signal processors. The decoder 17 decodes the payload to be transmitted to the upper layer. A received power estimator 18 estimates the received power using the signal that passed through the ADC 13 and signals being outputted from the digital signal processors 14, 15 and 16. The received power estimator 18 transmits the estimated received power to a gain controller 19. The gain controller 19 properly adjusts a gain for each stage such that the received power is in a desired range at multiple stages within the ADC 13 and the digital signal processors 14, 15 and 16. Since a new gain is calculated from the received signal having the gain thereof adjusted already, the scheme illustrated in FIG. 2 is called the closed loop gain control.
In accordance with the closed loop gain control, an entire gain control speed is affected by a plurality of factors such as a gain control step size, a power estimation algorithm and a gain settling time. The gain settling time is mostly caused by delay elements of the circuit in case of a properly designed circuit. A settling time of the analog filter 11, a latency of the ADC 13 and a settling time of memories of the digital signal processors 14, 15 and 16 also affect the gain settling time. For example, a time at which values of the memories in the closed loop of a gain control are filled with the received signal having a changed gain applied there to can become the same as the gain settling time. Particularly, since a storing time of the memories of the digital signal processors 14, 15 and 16 may be very long, a minimization of memory elements in the closed loop of the gain control is very important. Therefore, it is a general method to operate the digital signal processor that requires a long memory after a gain settling. For instance, an operation of a frequency shift estimation requires a relatively long memory, which is generally carried out after the gain control.
FIG. 3 is a diagram illustrating an example of the gain settling time in a digital filter wherein (a) illustrates an input signal of the digital filter and (b) illustrates an output signal of the digital filter. When a signal having its gain changed is applied to the digital filter, a distorted signal of an original signal is transmitted from a time at which the signal is applied until a predetermined time later, and an undistorted signal is outputted after the predetermined time. The distorted signal is referred to as a transient signal, and the transient signal is not used for a digital signal processing. Accordingly, digital signal processing is delayed until the transient signal disappears. Therefore, the gain settling time is elongated as a transient signal period gets longer, which prevents a rapid gain control.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.